A primary-alkyl-substituted sulfenic acid was synthesized and isolated by taking advantage of a cavity-shaped steric protection group and characterized by X-ray crystallographic analysis. The reactivities of the sulfenic acid toward various reagents were investigated, and it was demonstrated experimentally and theoretically that the addition of a sulfenic acid to a simple alkene to produce the corresponding sulfoxide is thermodynamically more favorable than the reverse reaction, i.e. syn-beta-elimination of a sulfoxide.